NAME
    Data::Graph::Util - Utilities related to graph data structure

VERSION
    This document describes version 0.005 of Data::Graph::Util (from Perl
    distribution Data-Graph-Util), released on 2019-02-14.

SYNOPSIS
     use Data::Graph::Util qw(toposort is_cyclic is_acyclic);

     # return nodes that satisfy the following graph: a must come before b, b must
     # come before c & d, and d must come before c.

     my @sorted = toposort(
         { a=>["b"], b=>["c", "d"], d=>["c"] },
     ); # => ("a", "b", "d", "c")

     # sort specified nodes (2nd argument) using the graph. nodes not mentioned in
     # the graph will be put at the end. duplicates are not removed.

     my @sorted = toposort(
         { a=>["b"], b=>["c", "d"], d=>["c"] },
         ["e", "a", "b", "a"]
     ); # => ("a", "a", "b", "e")

     # check if a graph is cyclic

     say is_cyclic ({a=>["b"]}); # => 0
     say is_acyclic({a=>["b"]}); # => 1

     # check if a graph is acyclic (not cyclic)

     say is_cyclic ({a=>["b"], b=>["c"], c=>["a"]}); # => 1
     say is_acyclic({a=>["b"], b=>["c"], c=>["a"]}); # => 0

DESCRIPTION
    Early release. More functions will be added later.

FUNCTIONS
    None are exported by default, but they are exportable.

  toposort
    Usage:

     toposort(\%graph[ , \@nodes ]) => sorted list

    Perform a topological sort on graph (currently using the Kahn
    algorithm). Will return the nodes of the graph sorted topologically.
    Will die if graph cannot be sorted, e.g. when graph is cyclic.

    If "\@nodes" is specified, will instead return @nodes sorted according
    to the topological order. Duplicates are allowed and not removed. Nodes
    not mentioned in graph are also allowed and will be put at the end.

  is_cyclic
    Usage:

     is_cyclic(\%graph) => bool

    Return true if graph contains at least one cycle. Currently implemented
    by attempting a topological sort on the graph. If it can't be performed,
    this means the graph contains cycle(s).

  is_acyclic
    Usage:

     is_acyclic(\%graph) => bool

    Return true if graph is acyclic, i.e. contains no cycles. The opposite
    of "is_cyclic".

HOMEPAGE
    Please visit the project's homepage at
    <https://metacpan.org/release/Data-Graph-Util>.

SOURCE
    Source repository is at
    <https://github.com/perlancar/perl-Data-Graph-Util>.

BUGS
    Please report any bugs or feature requests on the bugtracker website
    <https://rt.cpan.org/Public/Dist/Display.html?Name=Data-Graph-Util>

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.

SEE ALSO
    <https://en.wikipedia.org/wiki/Graph_(abstract_data_type)>

    <https://en.wikipedia.org/wiki/Topological_sorting#Kahn.27s_algorithm>

    Sort::Topological can also sort a DAG, but cannot handle cyclical graph.

AUTHOR
    perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2019, 2017, 2016 by perlancar@cpan.org.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.